(1) Field of the Invention
This invention generally relates to a control system located at a first site, such as a launching submarine, for guiding a steerable object, such as a torpedo, from that site toward a second site or target. More specifically, this invention relates to such a control system that operates even when both the first and second sites undergo independent motion.
(2) Description of the Prior Art
A launching submarine includes a control system for guiding a torpedo toward a target. In this particular application, the torpedo constitutes a steerable object while the submarine and target constitute first and second sites, respectively, that are capable of undergoing independent motion. One control system that has been used in submarine applications is a "corrected intercept" control system that guides a torpedo from the submarine, as the first site, toward the target, as the second site, on a collision course. Such intercept control systems generally operate with steerable objects additionally characterized by some internal homing or equivalent steering control system. In the case of a submarine launched torpedo, the corrected intercept control system directs a torpedo with an acoustic homing system toward the target. When the torpedo comes within the effective range of the homing system, steering control transfers to the homing system. Torpedoes that do not include such internal homing systems are directed to a final intercept or collision position solely by the steering control function.
Other diverse systems also control different torpedoes. In many, a wire is connected to the torpedo to maintain direct communications with a launcher submarine as the torpedo maneuvers toward a target. For example, U.S. Pat. No. 3,265,023 to Hollingsworth, Jr. et al. (1966) generally discloses the concept of maintaining communications over a wire connected between a torpedo and the launching vessel with the wire being paid out from a dispenser in the torpedo and in the launching vessel. U.S. Pat. No. 3,643,617 to Jones (1972) discloses an apparatus for guiding a torpedo along a collision course with a moving target ship. The torpedo maintains a predetermined substantially constant lead angle with respect to the target ship. The lead angle is maintained by constant adjustment of the torpedo speed as it travels toward an anticipated collision through guidance commands transferred over a communications wire. Another approach for guiding torpedoes toward a target is disclosed in U.S. Pat. No. 3,783,441 to Slawsky (1974). An air launched wire guided torpedo is controlled in response to sonobuoy signals received and processed on a surface vessel or aircraft. In this particular application communications are established through a buoy from which an electrical control cable connects to a torpedo.
Other control systems, particularly adapted for surface-to-surface or surface-to-air missiles, use a controller at one site proximate a launching site to establish a line of sight with a target. The control system maneuvers the missile along that line of sight. In U.S. Pat. No. 3,233,847 to Girsberger (1966) the line of sight defines a beam rider course, and the control system guides the remote controllable moving object along that beam rider course. The system operates by generating control guidance signals that continually correspond to a vectorial angular difference between an instantaneous line of sight to the moving object of target and an orientation axis.
U.S. Pat. No. 3,478,212 to Turck (1969) discloses an aiming system for the remote guidance of a self-propelled missile toward a target. This apparatus includes an orientable sighting instrument and an orientable electronic camera directly associated with the instrument adapted for emitting control signals for the missile and having a range of infrared spectral sensitivity different from that of the sighting instrument. An infrared source exposes both the target and the missile to radiation that embrace both ranges of sensitivity. The missile has reflecting filter means able to substantially absorb the infrared range corresponding the spectral sensitivity of this sighting means. The control system then operates on the missile to maintain a course along the line of sight beam between the launching point and the target.
U.S. Pat. No. 3,711,046 to Barhydt et al. (1973) discloses a missile guidance system in which a gunner establishes a line of sight from the gun position to the target. When a missile is launched, a source of pulsating radiant energy on the rear of the missile is detected by a guidance unit at the launching site. The guidance unit produces steering commands related to the deviation of the missile from the line of sight. Means, such as a wire interconnecting the guidance unit and the missile, transmit the guidance signals to the missile to direct it along the line of sight.
U.S. Pat. No. 4,008,869 to Weiss (1977) discloses a control system for projectile guidance and control for use against moving targets. This system (1) allows the projectile to fly a minimum energy path to target intercept, (2) applies corrective commands to the projectile as it approaches the target to correct the projectile in flight for errors in system "boresighting" and similar errors, and also to correct the ground control system on the basis of the same measurements so that these calibration errors will have a reduced degradation on the accuracy of subsequent projectiles, and (3) uses the miss sensing process to improve prediction accuracy when unguided projectiles are fired from the same launcher so that the system has both a controlled projectile and an unguided projectile capability, and both capabilities benefit from the miss sensing and data processing process.
U.S. Pat. No. 4,247,059 to Duke et al. (1981) discloses an automatic missile tracking and guidance system that guides a missile along a line of sight maintained by the operator with the target. The position of an infrared source disposed on the missile is detected. Guidance signals generated in accordance therewith control the flight of the missile along the line of sight. The infrared source comprises an array of semiconductor light emitting diodes.
U.S. Pat. No. 4,901,946 to Arnaud et al. (1990) discloses a system for guiding, by laser beam and pyrotechnic thrusters, of one of a number of carriers such as missiles which are intended to intercept maneuvering targets such as aircraft, helicopters or tanks. Guidance of the carrier is performed partly from the ground by means of a laser beam (beam-rider guidance) which tracks the target and partly be means of pyrotechnic thrusters placed on board the carrier. At each instant, the carrier "knows" its position with respect to the ideal flight path provided by the laser beam. The carrier corrects its flight path by triggering a pyrotechnic thruster when its distance with respect to the ideal flight path is greater than a predefined threshold value and when its radial velocity to the ideal path is lower than a predefined threshold.
U.S. Pat. No. 5,374,009 to Miller, Jr. et al. (1994) discloses an inertial guidance system for a missile that has no other guidance or inadequate terminal homing guidance to lock onto a target at the time of missile launch. A laser beam projected from the missile launch station is aimed toward the target. Light from the beam is reflected in random directions or scattered from aerosol particles that are ever present in the atmosphere. The scattered light strikes light detectors that are located on the sides of the missile. When the missile flies off the direction of the target, the amplitudes of impacting light on these detectors are different on different sides of the missile. Guidance controls activated by these amplitude differences cause the missile to veer toward the center of the beam and thus fly in a direction that is more toward the target.
Many of the foregoing references disclose a system known as a beam rider control system. That is, in each of many of the foregoing references a conventional control system directs a missile or torpedo along a bearing between the launching vehicle and the target. U.S. Pat. No. 5,436,832 to the inventors of this application discloses a beam rider guidance system for directing a steerable object, such as a torpedo, from a first site, such as a launching submarine, to a second site, such as a target. A guidance system senses the bearing between the first site and the second site and determines the bearing between the first site and the steerable object as it moves toward the second site. Various error signals are generated and classified into linguistic variables based upon membership functions of different sensed variable membership function sets to become fuzzy inputs to a fuzzy logic controller that produces fuzzy output membership functions from a control output membership function set based upon logical manipulation of the fuzzy inputs. These fuzzy control output membership functions are converted into an output having an appropriate form for control, subject to optional constraint to prevent unwanted trajectories. More specifically, this system measures the bearing to a guidance point, representing an effective position of detection for internal homing apparatus, and attempts to maintain the torpedo in an orientation by which the guidance point remains on the bearing line from the first site to the second site.
These and other related control systems are particularly adapted for guided missiles, torpedoes or other steerable objects wherein steering is smoothly variable between limits. However, there also exists a class of steerable objects that can only react to a limited number of prespecified course correction commands. For example, a torpedo might only be able to respond with course correction commands that define 2.degree. and 20.degree. port and starboard course changes. While the foregoing systems, including the fuzzy control guidance systems, provide improvements over conventional systems, even the fuzzy control systems are not readily adapted to provide a limited number of prespecified course correction commands.